small, sealed enclosure using Silver Flute woofers

[Bose(o)]

Hey guys/gals I haven't posted here in a looong time and it's actually my first time posting in the subwoofer section.

Anyhow, on to the nitty gritty. I have two 8" (W20RC38-04 that's the 4-ohm versions) Silver Flute woofers that have been sitting around collecting dust and since I've finalised my OB FR speakers I'd like to give these impressive guys the time they deserve.

I want the woofers to be setup in a dipole principle. I've searched everywhere for info on the pros/cons of pull-push and push-push so I will experiment with this once the enclosure has been made. Modelling the woofers in LSPCad and WinISD the enclosure size for a Qtc of 0.707 will be 17.0~17.4L. and, each driver will require ~52W to reach a maximum excursion of 5mm.. I forget exactly what the F3 was, but it wasn't at all impressive as it was near 70Hz.. Not foregetting to mention that the Fb was 100Hz. or so.

Having said that I'm not impressed with this setup, I'd like to venture into the famous Linkwitz Transform circuit. I've modelled a 15L. enclosure with a Linkwitz circuit resulting in an F3 of ~25hz.. The resonance of the circuit was 35Hz., the Q was the same as the enclosure and the DC gain was around 18dB..

I really have a lot of questions that will be revealed once I begin posting back and forth with you guys. The first one is: I remember reading something about excursion/power/equalization. It was some rule for i.e., and I think this is incorrect, if one equalizes 6dB. then the power required is twice as much and the excursion is four times as much. Where does this come from, what equation?

Also, everyone mentions "watch your excursion capabilities", but they don't say how. I know my drivers only have 5mm Xmax, but eq would be spread across the two drivers (wired in parallel, btw) equally, correct?

TIA, I know you guys can help me!

 

[hilbren]

The problem with linkwitz is that it's realy bad for drivers with a limmited xmax. The only thing the circuit does is amplify the frequenties your speaker is not suppose to handle.

So if you think xmax is going to be a problem, try using it without the linkwitz. dipoles sound cool anyway!


and if you want to calculate.. use a extreem big enclosure:
http://home.hccnet.nl/g.c.van.doorn/I/Linkxfrm axx1212.xls

 

[coolkhoa]

I'm no speaker expert, but I think you're better off with a ported box for a driver as small as an 8" for subwoofer duty (though I am unsure if the Silver Flute's specs are suitable for such a design). F3 in a sealed box is simply too high for most 8-inchers (as you noted), and IMO you shouldn't rely on LT to provide that much of an extension; the result could be greatly increased distortion for the woofer's limited Xmax, even with 2 woofers. For a living-room sub, I'd go with 10"+ drivers. I would venture to say that the Silver Flute is not the best option for a sub.

Just my $0.02.

 

[Bose(o)]

Ideally, if possible, I'd like to use my SFs with my Open Baffle loudspeakers which reach 50hz.. The pass-band or, operating range would then make it 20-50hz with high-order cross-overs to reduce distortion and power 'dissipation' to other frequencies. Do you think I could get away with LT?

Looking at the LT, with the circuit implemented, I can see that the result is a system that 'acts' as if the Q is what it isn't. However, the motion and physical characteristics of the woofer should be the same and by using another woofer I should be able to reduce the negative effects of equalization.

I looked at using ported woofers, but I detest ported woofers (mainly from a design point) after I experienced TL- and OB-bass. I know the LT is almost pointless as the enclosure size would decrease 2.4L only, but the response of the system would be incredible considering the size of the subwoofer. I was also looking at a TL design since the size doesn't matter, it's just that it would be nice to show off to family and friends. Although, ~11' tubes hung overhead would also be pretty darn sweet to show off.

I know there are better woofers out there, but it's just that I have these sitting here gathering dust. The wool cone is getting lonely and wants to produce some goodness.

 

[Otherwise]

Hi Bose(o), you asked if I could help.. Unfortunately I have to agree with coolkhoa, for the Silver Flutes i think a bass-reflex would be the way to go. The Q is low and with loose suspension and smallish x-max and all, the bass-reflex's tendency to decrease cone motion and produce higher spl sounds like a good plan.

Fs 31.0 Hz
Qms 1.51
Qes 0.27
Qts 0.23
Vas 72.3 Ltrs
X-max 5mm

Although, if you're listening at low levels most of the time (as am I) a closed box using two 8" units and a LT filter... mm it could actually work to some degree. In my system the max gain is around 19dB, the two 6,5"s reaching sub 40 Hz, maybe 30 Hz. I seldom reach 5mm cone movement, because of the low listening levels and usage as near-field monitors.. Power requirement has to be considered of course, for my speakers a 2x 45W amp was too small, it produced noticeable distortion at higher levels. If you give it a try, use sockets for the resistors and caps in the circuit so that xover freq and transform shape can be changed later if needed

If not best for your main system, those SFs could make a good computer sub, installed so that the magnets repel each other (back-to-back) thus creating a magnetic shielding

http://sound.westhost.com/project71.htm

 

[Bose(o)]

Okay, since LT+sealed isn't looking like a hot idea can one make a dipole woofer ported? I'd want the port facing down and I figure that the dipole characteristics inside the enclosure would also be lessened if not non-existent.

So many options to choose from.